1. Field of the Invention
The present invention relates to an inkjet recording apparatus for forming an image by using a recording head capable of discharging ink and, more specifically, relates to an inkjet recording apparatus capable of restoring a recording head and a maintenance method thereof.
2. Description of the Related Art
Along with recent wide use of information processors, such as personal computers, recording apparatuses used as image forming terminals have rapidly been improved and put to wide use. Among the various recording apparatuses, the recording apparatus most widely used by individual users is an inkjet recording apparatus. The inkjet recording apparatus prints images on recording media, such as paper, fabric, plastic sheets, and overhead projector (OHP) sheets, by discharging ink from ink outlets. The inkjet recording apparatus is in wide use because inkjet recording is significantly advantageous in that it is a low-noise and non-impact recording method, is easily applicable to color recording, and is low cost.
Basically, an inkjet recording apparatus records images by reproducing colors by subtractive color mixing using yellow ink, magenta ink, and cyan ink, which are the three primary colors of ink used in printing. More specifically, by mixing yellow ink and magenta ink, images in the orange or red color region can be reproduced. Similarly, by mixing yellow ink and cyan ink, the green region can be reproduced, and by mixing magenta ink and cyan ink, the blue or violet region can be reproduced.
The advancement in inkjet recording technology has improved the resolution, quality, and color of the recorded images, while reducing the cost. Along with the popularization of personal computers and digital cameras (including individual computers, digital cameras, and other integrated devices that have multiple functions in addition to the function as a computer or a digital camera, such as a cellular phone), inkjet recording apparatuses have greatly contributed to popularizing the use of recording apparatuses to individual users. However, such wide use of inkjet recording apparatuses has brought about a demand for improvements in the quality of the reproduced images. In order to respond to such demands from individual users, various improvements have been made.
For example, the contrast of the reproduced image has been improved and the reproduction of intermediate colors has been stabilized by applying an under color removal (UCR) process. In the UCR process, black (K) color components included in the color data for yellow (Y), magenta (M), and cyan (C) are extracted and replaced with black ink, which is used in addition to the three primary colors of ink, and the color components for Y, M, and C replaced by black ink are removed. Moreover, the graininess of the ink dots discharged onto a recording medium has been reduced, and the color gradation has been improved by using light cyan and light magenta ink in addition to yellow, magenta, cyan, and black ink.
Ink is composed of a color material such as dye or pigment. In particular, dye is superior in reproducing colors having high brightness.
In general, the recording head of an inkjet recording apparatus includes arrays of minute ink outlets. The ink outlets clog when unwanted materials, such as paper powder and dust, attach to the ink outlet unit or when ink dries and thickens and sticks to the ink outlet unit. As a result of clogging, the ink outlets discharge ink unsuccessfully (or even worse, will completely fail to discharge ink). Moreover, when an ink cartridge is used to supply ink to a brand-new recording head or when a brand-new recording head cartridge including an ink cartridge and a recording head is used, the ink channels and the ink outlets may not be in a satisfactory condition for discharging ink successfully since the ink channels, from the ink outlets of the recording head to the ink cartridge, are not filled with ink. Therefore, to clear clogging and to normalize the condition of ink channels, cleaning means for removing unwanted materials on the ink outlet unit (i.e. a surface of the recording head where ink outlets are formed. Hereinafter this surface is referred to as an ‘outlet surface’) and restoring means for normalizing the ink outlets and the ink channels of the recording head are provided.
Cleaning means is a mechanism for wipe-cleaning the outlet surface of the recording head with a flexible wiper. Restoring means includes a cap for covering the outlet surface and a pump that communicates with the cap and sucks out ink from inside the cap and the recording head. This structure of the restoring means enables preliminary discharge of ink from the ink outlets toward the cap by driving energy-generating elements disposed inside the ink outlets and restoration of the ink outlets by forcing the ink out of the ink outlets by contacting the cap with the outlet surface and sucking out the ink inside the recording head by suction force (negative pressure) generated by the pump. Preliminary discharge fills the ink channels and the recording head with ink, and restoration of ink outlets by suction removes dust and thickened ink from the recording head. As a result, the discharge of ink is maintained in good condition by eliminating the causes of ink discharge failure. Moreover, to reduce the possibility of ink discharge failure, the cap covers the ink outlets when the recording head is at a home position when recording is not carried out.
As the number of ink outlets increases, unwanted material is more likely to attach to the outlet surface. Therefore, it is desirable to perform restoration of the ink outlets to suck out unwanted ink and wipe-clean the outlet surface. However, if restoration of the ink outlets is performed more often than necessary, electricity consumption increases. Furthermore, wipe-cleaning interrupts the recording operation and, if performed more often than necessary, throughput decreases.
To prevent restoration by suction and wipe-cleaning to be carried out more often than necessary, known inkjet recording apparatuses count the number of discharges performed by the ink outlets and carry out restoration by suction and wipe-cleaning only when the number of discharges exceed a predetermined threshold value. As disclosed in Japanese Patent Laid Open No. 07-125228, a technology that enables wiping to be carried out for a suitable number of times by measuring the number of discharges and the duration of printing time and comparing these measured values with threshold values for measured values has been proposed. By counting the number of ink discharges in this way, the amount of ink remaining in the ink tank can also be calculated.
Recently, to form high quality images, a recording apparatus that uses other color inks in addition to cyan, magenta, yellow, and black (for example, red, green, and blue ink) and other liquids that become insoluble when mixed with ink have been proposed. However, as the number of different color inks and different types of liquids discharged from the recording head increases, the number of arrays of ink outlets has also increased. As a result, if all necessary arrays of ink outlets are formed on one recording element (semiconductor chip) as in known recording apparatuses, the recording element substrate becomes large and the cost for producing this recording element substrate without any defects becomes high.
A recording apparatus capable of forming high quality images using a known recording element substrate by providing two recording heads or by providing two recording element substrates on one recording head is known.
However, for a recording apparatus having two recording heads and two caps corresponding to the recording heads, if the number of discharges from a first recording heads exceeds a predetermined threshold value and the number of discharges from a second recording head is just below the predetermined threshold value, a suction flag is set for only the first recording head. Thus, restoration of the ink outlets by suction is carried out on only the first recording head having set a suction flag. Then, if recording is performed for a short time after the restoration of the first recording head, the second recording head will set a suction flag and restoration will be carried out for the second recording head. In other words, restoration is carried out two times within a short period of time, taking up time for maintaining the recording head and reducing throughput. Moreover, since the restoration operation is carried out twice, the waiting time for completing the recording becomes longer and a large amount of ink may be sucked away, causing inconvenience to users.